Dual output laser diode

ABSTRACT

A dual output laser diode may include first and second end facets and an active section. The first and second end facets have low reflectivity. The active section is positioned between the first end facet and the second end facet. The active section is configured to generate light that propagates toward each of the first and second end facets. The first end facet is configured to transmit a majority of the light that reaches the first end facet through the first end facet. The second end facet is configured to transmit a majority of the light that reaches the second end facet through the second end facet.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation-in-part of U.S. patentapplication Ser. No. 16/947,643, filed Aug. 11, 2020. The aforementionedapplication is hereby incorporated by reference in its entirety.

FIELD

The embodiments discussed herein relate to a dual output laser diode.

BACKGROUND

Unless otherwise indicated in the present disclosure, the materialsdescribed in the present disclosure are not prior art to the claims inthe present application and are not admitted to be prior art byinclusion in this section.

Doped fiber amplifiers generally operate by energizing ions in a dopedfiber with pump light from a pump laser diode. An optical signal at adifferent wavelength than the pump light is transmitted through thedoped fiber. Photons of the optical signal interact with the energizedions, causing the ions to give up some of their energy in the form ofphotons at the same wavelength as the photons of the optical signal,with the ions returning to a lower energy state. The optical signal isthereby amplified as it passes through the doped fiber.

The subject matter claimed in the present disclosure is not limited toimplementations that solve any disadvantages or that operate only inenvironments such as those described above. Rather, this background isonly provided to illustrate one example technology area where someimplementations described in the present disclosure may be practiced.

SUMMARY

This Summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential characteristics of the claimed subject matter, nor is itintended to be used as an aid in determining the scope of the claimedsubject matter.

In an example, a dual output laser diode may include first and secondend facets and an active section. The first end facet has lowreflectivity. The second end facet has low reflectivity. The activesection is positioned between the first end facet and the second endfacet. The active section is configured to generate light thatpropagates toward each of the first and second end facets. The first endfacet is configured to transmit a majority of the light that reaches thefirst end facet through the first end facet. The second end facet isconfigured to transmit a majority of the light that reaches the secondend facet through the second end facet.

In another example, a dual fiber amplifier system may include first andsecond fiber amplifiers and a dual output laser diode. The first fiberamplifier includes a first pump input optical fiber. The second fiberamplifier includes a second pump input optical fiber. The dual outputlaser diode includes first and second end facets and an active section.The first end facet has low reflectivity and is optically coupled to thefirst pump input optical fiber. The second end facet has lowreflectivity and is positioned opposite the first end facet andoptically coupled to the second pump input optical fiber. The activesection is positioned between the first end facet and the second endfacet. The active section is configured to generate pump light inresponse to injection of an electrical drive signal into the activesection. The pump light is configured to propagate toward each of thefirst and second end facets. The first end facet is configured totransmit a portion of the pump light that reaches the first end facetthrough the first end facet. The first pump input optical fiber ispositioned to receive the portion of the pump light that passes throughthe first end facet. The second end facet is configured to transmit aportion of the pump light that reaches the second end facet through thesecond end facet. The second pump input optical fiber is positioned toreceive the portion of the pump light that passes through the second endfacet.

In another example, a method may include injecting an electrical drivesignal into an active section of a dual output laser diode. The activesection may be positioned between a first end facet and a second endfacet of the dual output laser diode. The method may include generatinglight in the active section of the dual output laser diode responsive toinjection of the electrical drive signal. The method may includepropagating the light toward each of the first and second end facets.The method may include transmitting a majority of the light that reachesthe first end facet through the first end facet. The method may includetransmitting a majority of the light that reaches the second end facetthrough the second end facet.

Additional features and advantages of the invention will be set forth inthe description which follows, and in part will be obvious from thedescription, or may be learned by the practice of the invention. Thefeatures and advantages of the invention may be realized and obtained bymeans of the instruments and combinations particularly pointed out inthe appended claims. These and other features of the present inventionwill become more fully apparent from the following description andappended claims, or may be learned by the practice of the invention asset forth hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

To further clarify the above and other advantages and features of thepresent invention, a more particular description of the invention willbe rendered by reference to specific embodiments thereof which areillustrated in the appended drawings. It is appreciated that thesedrawings depict only typical embodiments of the invention and aretherefore not to be considered limiting of its scope. The invention willbe described and explained with additional specificity and detailthrough the use of the accompanying drawings in which:

FIG. 1A illustrates an example dual fiber amplifier system that includesa dual output laser diode;

FIG. 1B illustrates a portion of the dual fiber amplifier system of FIG.1A that includes the dual output laser diode and first and second pumpinput optical fibers;

FIG. 2 is a cross-sectional view of an example dual output laser diode;

FIG. 3 is a top view of another example dual output laser diode; and

FIG. 4 is a top view of another example dual output laser diode,

all arranged in accordance with at least one embodiment describedherein.

DETAILED DESCRIPTION

Embodiments described herein relate to a dual output laser diode thatgenerally includes an active section positioned between two end facets,each of which has low reflectivity. For example, each of the end facetsmay have an anti-reflection (AR) coating. In comparison, other laserdiodes typically include an AR coating on only one end facet with a highreflectivity (HR) coating on the other end facet to direct substantiallyall light generated in the laser diode through the end facet with the ARcoating.

Example dual output laser diodes described herein may be implementedwith fiber amplifier systems such as erbium-doped fiber amplifier (EDFA)systems or other systems. Some fiber amplifier systems pump multipledoped fibers with pump light from a single laser diode. In particular,the pump light may be split into multiple paths using one or moreoptical components external to the laser diode. Splitting the pump lightexternally to the laser diode may result in pump instability due tocoherent interactions and other effects.

According to embodiments described herein, the pump light is effectivelysplit internally in the laser diode, e.g., by configuring each end facetwith a low reflectivity such that some pump light exits each end facetand may be directed into a corresponding path. This arrangement mayavoid or at least reduce pump instability due to coherent interactionsand other effects that may arise when the pump light is output from oneend facet of the laser diode and is split externally to the laser diode.

In addition, this arrangement may decrease a maximum optical powerdensity within the laser diode by a factor of about two since no pumplight or relatively little pump light is reflected at one end facet backto the other as occurs in, e.g., laser diodes with an AR coating at oneend facet and an HR coating at the other. The reduced maximum opticalpower density of laser diodes according to embodiments described hereinrelative to laser diodes with AR and HR coatings at opposite end facetsmay increase reliability.

In an embodiment, the dual output laser diode may output equal or aboutequal pump light power from the end facets.

In an embodiment, the dual output laser diode may output unequal pumplight power from the end facets. Unequal pump light power may beachieved with AR coatings of unequal reflectivity at the end facets,such as a first AR coating with a reflectivity of 1% at a first endfacet and a second AR coating with a reflectivity of 0.75% at a secondend facet. Alternatively or additionally, unequal pump light power atthe end facets may be achieved by structuring a waveguide of the laserdiode to have different transmissivities at or near the two end facets,such as a transmissivity of 99.5% for a portion of the waveguide nearthe first end facet and a transmissivity of 99% for a portion of thewaveguide near the second end facet.

Alternatively or additionally, unequal pump light power at the endfacets may be achieved by independently controlling first and secondportions of the dual output laser diode. In this and other embodiments,the dual output laser diode may include a first anode and cathodeelectrically coupled to the first portion of the laser diode and asecond anode and cathode electrically coupled to the second portion ofthe laser diode. An etched mirror, a distributed feedback (DFB) mirror,or other reflective structure may be formed in the laser diode betweenthe first and second portions to optically isolate the first and secondportions from each other. Accordingly, the first portion of the laserdiode and the second portion of the laser diode may be independentlyoperated while being integrally formed in a single structure.

Reference will now be made to the drawings to describe various aspectsof example embodiments of the invention. It is to be understood that thedrawings are diagrammatic and schematic representations of such exampleembodiments, and are not limiting of the present invention, nor are theynecessarily drawn to scale.

FIG. 1A illustrates an example dual fiber amplifier system 100A(hereinafter “system 100A”) that includes a dual output laser diode 102(hereinafter “laser 102”), arranged in accordance with at least oneembodiment described herein. The system 100A may further include firstand second fiber amplifiers 104A, 104B (collectively “fiber amplifiers104” or generically “fiber amplifier 104”). The fiber amplifiers 104include respective pump paths 106A, 106B (collectively “pump paths 106”or generically “pump path 106”) that may include optical fibers or othersuitable waveguides to convey pump light from the laser 102 into thecorresponding one of the fiber amplifiers 104. When implemented asoptical fibers, the pump paths 106 may be referred to as pump inputoptical fibers.

In general, the laser 102 may include two end facets and may beconfigured to output pump light from each of the two end facets into acorresponding one of pump paths 106. For example, a portion, e.g., someor most, of the pump light that reaches each end facet may betransmitted through the end facet and a corresponding pump input opticalfiber of the pump paths 106 may be positioned to receive the portion ofthe pump light that passes through the corresponding end facet.Configuring the laser 102 to output pump light from both end facets mayeliminate the need for any components external to the laser 102 to splitpump light as required for laser diodes that have a HR coating at oneend facet with pump light output only from the other end facet.

Each fiber amplifier 104 may include an input optical tap 108A, 108B(hereinafter collectively “input taps 108” or generically “input tap108”), an input photodiode 110A, 110B (hereinafter collectively “inputphotodiodes 110” or generically “input photodiode 110”), a first opticalisolator 112A, 112B (hereinafter collectively “first isolators 112” orgenerically “first isolator 112”), a beam combiner 114A, 114B(hereinafter collectively “combiners 114” or generically “combiner114”), a doped fiber 116A, 116B (hereinafter collectively “doped fibers116” or generically “doped fiber 116”), a second optical isolator 118A,118B (hereinafter collectively “second isolators 118” or generically“second isolator 118”), an output optical tap 120A, 120B (hereinaftercollectively “output taps 120” or generically “output tap 120”), and anoutput photodiode 122A, 122B (hereinafter collectively “outputphotodiodes 122” or generically “output photodiode 122”). In general,each fiber amplifier 104 is configured to receive an optical signal S₁or S₂ as input and to output an amplified signal S_(1A) or S_(2A) whichis an amplified version of the optical signal S₁ or S₂ respectively.

In more detail, the optical signal S₁ or S₂ is received at the input tap108 and a small portion thereof (e.g., 2%) is directed by the input tap108 to the input photodiode 110 to, e.g., measure optical power of theoptical signal S₁ or S₂. A remainder (e.g., 98%) of each of the opticalsignals S₁ or S₂ passes through the input tap 108 and the first isolator112 to the combiner 114. The first isolator 112 may be configured toprevent or at least reduce back reflection from the combiner 114. Thecombiner 114 combines the optical signal S₁ or S₂ with the pump lightreceived from the laser 102 via the pump path 106.

Each optical signal S₁ or S₂ has a wavelength λ_(1In) or λ_(2In). Thevalues of λ_(1In) and λ_(2In) may be the same or different. The pumplight received at the combiner 114 has a wavelength λ_(1Pump) orλ_(2Pump). The values of λ_(1Pump) and λ_(2Pump) may be the same ordifferent. Further, the values of λ_(1Pump) and λ_(2Pump) are selectedto provide Optical amplification to the corresponding optical signal S₁or S₂ operating, at λ_(1In) or λ_(2In) in the presence of a specificrare-earth dopant within the doped fiber 116. The dopant may be erbium,ytterbium, or other dopant. When the dopant is erbium, the wavelengthλ_(1Pump) or λ_(2Pump) of the pump light emitted by the laser 102 may beabout 980 nanometers (nm) (e.g., 970 nm to 990 nm), such as a wavelengthof 972 nm, 974 nm, 976 nm, or 978 nm. In some embodiments, pump light atthe wavelengths λ_(1Pump) or λ_(2Pump) of about 980 nanometers may beconfigured to provide amplification in the doped fiber 116 to theoptical signals S₁ or S₂ when the wavelengths λ_(1In) or λ_(2In) of theoptical signals S₁ and S₂ are about 1550 nm, such as wavelengths in theC band (˜1535 nm to 1565 nm), or about 1590 nm, such as wavelengths inthe L band (˜1565 nm to 1625 nm).

The combiner 114 outputs the optical signal S₁ or S₂ combined with thepump light to the doped fiber 116. The pump light at wavelengthλ_(1Pump) or λ_(2Pump) energizes ions in the doped fiber 116 and theoptical signal S₁ or S₂ at wavelength λ_(1In) or λ_(2In) interacts withthe energized ions. In particular, photons of the optical signal S₁ orS₂ at the wavelength λ_(1In) or λ_(2In) stimulate emission of photonsfrom the energized ions at the wavelength λ_(1In) or λ_(2In) to generatethe amplified signal S_(1A) or S_(2A).

The amplified signal S_(1A) or S_(2A) passes through the second isolator118 to the output tap 120. The output tap 120 directs a small portion ofthe amplified signal S_(1A) or S_(2A) to the output photodiode to, e.g.,measure optical power of the amplified signal S_(1A) or S_(2A). Theremainder of the amplified signal S_(1A) or S_(2A) passes through theoutput tap 120 and is output from the fiber amplifier 104.

The system 100A may additionally include one or more controllers 124A,124B (hereinafter collectively “controllers 124” or generically“controller 124”) and one or more laser drivers 126A, 126B (hereinaftercollectively “laser drivers 126” or generically “laser driver 126”)(“LD” in FIG. 1A). The controller 124 may be communicatively coupled tothe input photodiode 110 and the output photodiode 122. The laser driver126 may be communicatively coupled to the controller 124 and the laser102. The laser driver 126 is generally configured to apply an electricaldrive signal to the laser 102 as directed by the controller 124. Opticalpower of the pump light emitted by the laser 102 may be determined bythe electrical drive signal. For example, the laser 102 may emit pumplight with an optical power that is proportional to or has some otherknown relationship to current of the electrical drive signal.

The controller 124 may compare the optical power of the optical signalS₁ or S₂, e.g., as measured by the input photodiode 110, to the opticalpower of the amplified signal S_(1A) or S_(2A), e.g., as measured by theoutput photodiode 122, to determine gain of the fiber amplifier 104. Ifthe gain is above or below a target gain, the laser driver 126 mayadjust the electrical drive signal to increase or decrease the gain ofthe fiber amplifier 104. In some embodiments described herein, the laser102 includes two portions that may be independently controlled by acorresponding one of the laser drivers 126 to independently control gainin the fiber amplifiers 104.

FIG. 1A illustrates an example in which the optical power of the pumplight from the two end facets of the laser 102 is independentlycontrolled, e.g., by providing independent electrical drive signals fromindependent laser drivers 126 to independent portions of the laser 102.In other embodiments, the optical power of the pump light from the twoend facets may not be independent from the other. In these and otherembodiments, the system 100A may have a single controller 124 and asingle laser driver 126 rather than two controllers 124 and two laserdrivers 126.

FIG. 1B illustrates a portion 100B of the system 100A of FIG. 1A thatincludes the laser 102 and first and second pump input optical fibers128A, 128B (hereinafter collectively “pump input optical fibers 128” orgenerically “pump input optical fiber 128”), arranged in accordance withat least one embodiment described herein. The pump input optical fibers128 may include, be included in, or correspond to the pump paths 106 ofFIG. 1A.

As illustrated in FIG. 1B, the laser 102 includes two end facets 130A,130B (hereinafter collectively “end facets 130” or generically “endfacet 130”) spaced apart from each other. Each of the end facets 130 haslow reflectivity, such as a reflectivity of 5%, 3%, or 1% or less. Thereflectivity may be or include reflectivity for a single wavelength,multiple wavelengths, or across a range of wavelengths such as anoperational wavelength range of the laser 102. The operationalwavelength range may include wavelengths suitable for pump light, suchas wavelengths of about 980 nm or other wavelengths. In someembodiments, the operational wavelength range may be from 970 nm to 990nm, or from 975 nm to 985 nm, or other suitable range.

The pump input optical fibers 128 are positioned so that thecorresponding end facet 130 is optically coupled to the correspondingpump input optical fiber 128. For example, the first end facet 130A isoptically coupled to the first pump input optical fiber 128A and thesecond end facet 130B is optically coupled to the second pump inputoptical fiber 128B. In some embodiments, each pump input optical fiber128 may be optically aligned to the corresponding end facet 130 andpositioned sufficiently close to the corresponding end facet 130 thatpump light output from the first end facet 130A is coupled into the pumpinput optical fiber 128. Alternatively or additionally, one or moreoptical elements, such as one or more lenses or other optical elements,may be positioned between the end facet 130 and the pump input opticalfiber 128.

Each of the pump input optical fibers 128 may include a first or secondfiber Bragg grating (FBG) 132A, 132B (hereinafter collectively “FBGs132” or generically “FBG 132”) formed therein. The FBGs 132 may beconfigured to reflect a portion, e.g., 2-4%, of the pump light back tothe laser 102. Each FBG 132 may be configured to reflect back apredetermined wavelength or multiple predetermined wavelengths which may“lock” the laser 102 to the predetermined wavelength(s) such that thelaser 102 exhibits stable lasing at the predetermined wavelength(s). TheFBGs 132 may be configured to reflect back the same or differentpredetermined wavelength(s), to cause the laser 102 to emit pump lightfrom the end facets 130 at the same or different predeterminedwavelength(s).

For example, the first FBG 132A may be configured to reflect back afirst wavelength of 974 nm. The reflected light may be coupled throughthe first end facet 130A into the laser 102 where it interacts generallywith a first portion 134A of the laser 102 such that the first portion134A of the laser 102 is locked to 974 nm.

The second FBG 132B may be configured to reflect back both the firstwavelength of 974 nm and a second wavelength of 976 nm. The reflectedlight may be coupled through the second end facet 130B into the laser102 where it interacts generally with a second portion 134B of the laser102 such that the second portion 134B of the laser 102 is locked to both974 nm and 976 nm.

More generally, each FBG 132 may lock the corresponding first or secondportion 134A, 134B of the laser 102 to one or multiple predeterminedwavelength(s).

In other embodiments, the laser 102 itself may include a DFB structureto lock the laser 102 to a predetermined wavelength(s) such that theFBGs 132 may be omitted.

In some embodiments, each of the FBGs 132 forms a fiber cavity with thelaser 102, the FBGs 132 providing sufficient reflectivity to ensurelasing of the laser 102. Alternatively or additionally, the laser 102may include a ridge structure as described with respect to FIG. 2 .Roughness of the ridge structure, thermal induced refractive changes, orgain induced refractive changes along the length of the laser 102 mayreflect and scatter light generated in the laser 102 sufficiently tobuild up the optical field and ensure lasing of the laser 102. In someembodiments, the laser 102 may have a higher threshold or gain forlasing than other lasers in view of the low reflectivity at the endfacets 130.

FIG. 2 is a cross-sectional view of an example dual output laser diode200 (hereinafter “laser 200”), arranged in accordance with at least oneembodiment described herein. The laser 200 may include, be included in,or correspond to the other lasers herein. The cross-sectional view ofFIG. 2 is in a plane that is parallel to end facets of the laser 200 andperpendicular to a light emission direction of the laser 200. The lightemission direction is in and out of the page in FIG. 2 and thisdirection is also referred to as a longitudinal direction.

As illustrated in FIG. 2 , the laser 200 and laser diodes generally mayinclude various epitaxial layers, such as a substrate 202, a lowercladding layer 204, a lower waveguide layer 206, an active layer 208, anupper waveguide layer 210, an upper cladding layer 212, a cathode 214,and an anode 216. The laser 200 may include additional or differentlayers or elements than illustrated in FIG. 2 in other embodiments. Theend facets of the laser 200 may be formed in the epitaxial layers, e.g.,by cleaving through the epitaxial layers.

The configuration of FIG. 2 includes the active layer 208 with multiplequantum wells (MQWs) embedded in the lower and upper waveguide layers206, 210 and surrounded by lower and upper cladding layers 204, 212 thatare configured to confine the optical mode in a transversal direction,e.g., vertically in FIG. 2 .

The laser 200 includes a ridge structure 218 to confine the optical modein a lateral direction, e.g., horizontally in FIG. 2 . The ridgestructure 218 with lower and upper waveguide layers 206, 210 and lowerand upper cladding layers 204, 212 forms a waveguide that extendslongitudinally, e.g., in and out of the page in FIG. 2 , between endfacets of the laser 200 and that is configured to guide light generatedby the laser 200.

The active layer 208 may extend longitudinally for all or a portion of alength (e.g., in and out of the page in FIG. 2 ) of the laser 200.Alternatively or additionally, the anode 216 may extend longitudinallyfor all or a portion of the length of the laser 200 and the anode 216may have a region in which current is injected, referred to as a currentinjection region, that may extend longitudinally for all or a portion ofa length of the anode 216. A length of the current injection region maydetermine a longitudinal extent of stimulated emission of light withinthe laser 200. A portion of the laser 200 that extends longitudinallythe length of the active layer 208, the length of the anode 216, or thelength of the current injection region of the anode 216 may be referredto as an active section of the laser 200. The active section of thelaser 200 may, but does not necessarily, extend longitudinally from oneend facet to the other.

The cathode 214 and the anode 216 are electrically coupled to oppositesides of the active section. In the example of FIG. 2 , the cathode 214and the anode 216 are electrically coupled in particular to a bottom andtop of the active section of the laser 200. A laser driver, such as thelaser driver 126 of FIG. 1A, may be coupled to the anode 216 to injectan electrical drive signal into and through the laser 200 to the cathode214. The electrical drive signal may cause electrons and holes to beinjected from opposite sides into the active layer 208 where theyrecombine via stimulated emission to generate photons.

FIG. 3 is a top view of another example dual output laser diode 300(hereinafter “laser 300”), arranged in accordance with at least oneembodiment described herein. The laser 300 may include, be included in,or correspond to the other lasers herein. As illustrated in FIG. 3 , thelaser 300 may include a first end facet 302, a second end facet 304, andan active section 306 positioned between the first end facet 302 and thesecond end facet 304.

In general, the active section 306 may be configured to generate lightthat propagates toward each of the first and second end facets 302, 304.The light may be generated by the active section 306 in response toinjection of an electrical drive signal into the active section 306. Thelaser 300 may further include an anode 308 and a cathode 310electrically coupled to opposite sides, e.g., a top and bottom, of theactive section 306 to inject the electrical drive signal into the activesection 306 between the anode 308 and the cathode 310.

Each of the first and second end facets 302, 304 may have lowreflectivity. In an example, the low reflectivity at each of the firstand second end facets 302, 304 is achieved by cleaving the laser 300from a wafer of lasers 302 and forming an AR coating on the cleaved endfacets.

In these and other embodiments, the first and second end facets 302, 304may be configured to transmit a portion, such as a majority, of thelight generated by the active section 306 that reaches the first orsecond end facet 302, 304 through the first or second end facet 302,304. For example, the first or second end facet 302, 304 may beconfigured to transmit at least 95%, 97%, or 99% of the light generatedby the active section 306 that reaches the first or second end facet302, 304 through the first or second end facet 302, 304. In these andother embodiments, the first or second end facet 302, 304 may have areflectivity less than 1%. The reflectivity may be or includereflectivity for a single wavelength, multiple wavelengths, or a rangeof wavelengths such as an operational wavelength range of the laser 300.The operational wavelength range of the laser 300 may be the same as ordifferent than other operational wavelength ranges described herein.

In some embodiments, the reflectivity of the first end facet 302 is thesame as the reflectivity of the second end facet 304. Accordingly, theoptical power of light output from the first and second end facets 302,304 may be the same or approximately the same.

In some embodiments, the reflectivity of the first end facet 302 isdifferent than the reflectivity of the second end facet 304.Accordingly, the optical power of light output from the first end facet302 may be different than the optical power of light output from thesecond end facet 304.

The active section 306 may include a waveguide 312 that extends betweenthe first end facet 302 and the second end facet 304. The waveguide 312may include the waveguide described with respect to FIG. 2 or othersuitable waveguide. A first portion 314 of the waveguide 312 near thefirst end facet 302 may have a first transmissivity. A second portion316 of the waveguide 312 near the second end facet 304 may have a secondtransmissivity. The first and second transmissivities may each be orinclude transmissivity for a single wavelength, multiple wavelengths, ora range of wavelengths such as the operational wavelength range of thelaser 300. In these and other embodiments, the first and secondtransmissivities may be greater than 95%, 97%, or 99%.

The first and second transmissivities of the first and second portions314, 316 of the waveguide 312 may be the same or different. The firstand second transmissivities may depend on materials and structure of thefirst and second portions 314, 316 of the waveguide 312. Accordingly,the materials or structure of the first and second portions 314, 316 ofthe waveguide 312 may be selected to output light with equal ordifferent optical power from the first and second end facets 302, 304,as desired.

FIG. 4 is a top view of another example dual output laser diode 400(hereinafter “laser 300”), arranged in accordance with at least oneembodiment described herein. The laser 400 may include, be included in,or correspond to the other lasers herein. As illustrated in FIG. 4 , thelaser 400 may include a first end facet 402, a second end facet 404, andan active section 406 positioned between the first end facet 402 and thesecond end facet 404. The laser 400 may additionally include a waveguide408. The first and second end facets 402, 404, the active section 406,and the waveguide 408 may generally be configured and operated in thesame or similar manner as the corresponding components in other lasersdescribed herein.

The laser 400 may additionally include a reflective structure 410 formedin the active section 406 between first and second portions 412, 414 ofthe active section 406. The reflective structure 410 may be configuredto optically isolate the first portion 412 of the active section 406from the second portion 414 of the active section 406. The reflectivestructure 410 may include an etched mirror, a DFB structure, or othersuitable structure formed in the active section 406. When implemented asa DFB structure, the reflective structure 410 may lock the laser 400 toa predetermined wavelength(s).

A placement of the reflective structure 410 within the active section406 may be selected to divide the active section 406 into portions ofequal or unequal length. For example, as illustrated in FIG. 4 , thefirst portion 412 is longer than the second portion 414. In general,greater active section length leads to greater optical power output, allother parameters being equal. Accordingly, another option to provideunequal optical power at the end facets of a dual output laser diode, ifdesired, is to configure the dual output laser diode with an activesection with two portions of unequal length as illustrated in FIG. 4 .

The laser 400 may further include a first anode and cathode 416, 418electrically coupled to the first portion 412 of the active section 406and a second anode and cathode 420, 422 electrically coupled to thesecond portion 414 of the active section 406. In particular, the firstanode and cathode 416, 418 may be electrically coupled to opposite sides(e.g., top and bottom) of the first portion 412 of the active section406 and the second anode and cathode 420, 422 may be electricallycoupled to opposite sides (e.g., top and bottom) of the second portion414 of the active section 406. A first electrical drive signal may beinjected through the first portion 412 via the first anode and cathode416, 418 and a second electrical drive signal may be injected throughthe second portion 414 via the second anode and cathode 420, 422.Accordingly, while the first and second portions 412, 414 of the activesection 406 are integrally formed in a single structure (e.g., anepitaxial structure of the laser 400), they may nevertheless beindependently operated.

An example method to operate a dual output laser diode or a dual fiberamplifier system will now be described. The dual output laser diode mayinclude any of the lasers 102, 200, 300, 400 or other lasers describedherein. The dual fiber amplifier system may include the system 100A orother dual fiber amplifier systems described herein.

The method may include injecting an electrical drive signal into anactive section of a dual output laser diode, the active sectionpositioned between a first end facet and a second end facet of the dualoutput laser diode. Injecting the electrical drive signal into theactive section may include injecting a single electrical drive signalinto the active section, e.g., via the anode 216, 310 and cathode 214,308 of FIGS. 2-3 .

Alternatively or additionally, injecting the electrical drive signalinto the active section may include injecting a first electrical drivesignal into a first portion of the active section, e.g., the firstportion 412 of FIG. 4 via the first anode and cathode 416, 418, andinjecting a second electrical drive signal into a second portion of theactive section, e.g., the second portion 414 of FIG. 4 via the secondanode and cathode 420, 422. The first portion of the active section maybe optically isolated from the second portion of the active section,e.g., by a reflective structure such as the reflective structure 410 ofFIG. 4 .

The method may include generating light in the active section of thedual output laser diode responsive to injection of the electrical drivesignal.

The method may include propagating the light toward each of the firstand second end facets. In particular, some of the generated light may bepropagated toward the first end facet and some of the generated lightmay be propagated toward the second end facet.

The method may include transmitting a majority of the light that reachesthe first end facet through the first end facet. Transmitting themajority of the light that reaches the first end facet through the firstend facet may include transmitting at least 99% of the light thatreaches the first end facet through the first end facet.

The method may include transmitting a majority of the light that reachesthe second end facet through the second end facet. Transmitting themajority of light that reaches the second end facet through the secondend facet may include transmitting at least 99% of the light thatreaches the second end facet through the second end facet.

In some embodiments, the method may also include coupling lighttransmitted through the first end facet into a first pump input opticalfiber of a first fiber amplifier and coupling light transmitted throughthe second end facet into a second pump input optical fiber of a secondfiber amplifier. The method may further include operating each of thefirst and second fiber amplifiers, e.g., as described with respect toFIG. 1A.

Unless specific arrangements described herein are mutually exclusivewith one another, the various implementations described herein can becombined in whole or in part to enhance system functionality or toproduce complementary functions. Likewise, aspects of theimplementations may be implemented in standalone arrangements. Thus, theabove description has been given by way of example only and modificationin detail may be made within the scope of the present invention.

With respect to the use of substantially any plural or singular termsherein, those having skill in the art can translate from the plural tothe singular or from the singular to the plural as is appropriate to thecontext or application. The various singular/plural permutations may beexpressly set forth herein for sake of clarity. A reference to anelement in the singular is not intended to mean “one and only one”unless specifically stated, but rather “one or more.” Moreover, nothingdisclosed herein is intended to be dedicated to the public regardless ofwhether such disclosure is explicitly recited in the above description.

In general, terms used herein, and especially in the appended claims(e.g., bodies of the appended claims) are generally intended as “open”terms (e.g., the term “including” should be interpreted as “includingbut not limited to,” the term “having” should be interpreted as “havingat least,” the term “includes” should be interpreted as “includes but isnot limited to,” etc.). Furthermore, in those instances where aconvention analogous to “at least one of A, B, and C, etc.” is used, ingeneral, such a construction is intended in the sense one having skillin the art would understand the convention (e.g., “a system having atleast one of A, B, and C” would include but not be limited to systemsthat include A alone, B alone, C alone, A and B together, A and Ctogether, B and C together, or A, B, and C together, etc.). Also, aphrase presenting two or more alternative terms, whether in thedescription, claims, or drawings, should be understood to include one ofthe terms, either of the terms, or both terms. For example, the phrase“A or B” will be understood to include the possibilities of “A” or “B”or “A and B.”

The present invention may be embodied in other specific forms withoutdeparting from its spirit or essential characteristics. The describedembodiments are to be considered in all respects only as illustrativeand not restrictive. The scope of the invention is, therefore, indicatedby the appended claims rather than by the foregoing description. Allchanges which come within the meaning and range of equivalency of theclaims are to be embraced within their scope.

What is claimed is:
 1. A dual output laser diode, comprising: an activesection positioned between a first end facet and a second end facet; anda reflective structure formed in the active section between a firstportion of the active section and a second portion of the activesection, wherein the reflective structure is configured to opticallyisolate the first portion of the active section from the second portionof the active section.
 2. The dual output laser diode of claim 1,wherein the active section comprises a waveguide having a first portionnear the first end facet and a second portion near the second end facet,and wherein a first transmissivity of the first portion of the waveguideis different than a second transmissivity of the second portion of thewaveguide.
 3. The dual output laser diode of claim 2, wherein the firsttransmissivity and the second transmissivity is across an operationalwavelength range.
 4. The dual output laser diode of claim 1, wherein theactive section is configured to generate light that propagates towardeach of the first end facet and the second end facet.
 5. The dual outputlaser diode of claim 1, wherein the reflective structure formed in theactive section comprises an etched mirror or a distributed feedback(DFB) structure.
 6. The dual output laser diode of claim 1, wherein thefirst portion of the active section has a first length and the secondportion of the active section has a second length unequal to the firstlength.
 7. The dual output laser diode of claim 1, wherein the firstportion of the active section and the second portion of the activesection are integrally formed in a single epitaxial structure.
 8. Thedual output laser diode of claim 1, further comprising: a first anodeand a first cathode electrically coupled to opposing sides of the firstportion of the active section; and a second anode and a second cathodeelectrically coupled to opposing sides of the second portion of theactive section.
 9. The dual output laser diode of claim 8, wherein thefirst anode overlaps the first portion of the active section, andwherein the second anode overlaps the second portion of the activesection.
 10. The dual output laser diode of claim 8, wherein the firstcathode is spaced apart from the first portion of the active section,and wherein the second cathode is spaced apart from the second portionof the active section.
 11. A dual fiber amplifier system, comprising: afirst fiber amplifier that includes a first pump input optical fiber; asecond fiber amplifier that includes a second pump input optical fiber;and a dual output laser diode that includes: an active sectionpositioned between a first end facet and a second end facet; and areflective structure formed in the active section between a firstportion of the active section and a second portion of the activesection, the reflective structure being configured to optically isolatethe first portion of the active section from the second portion of theactive section.
 12. The dual fiber amplifier system of claim 11, whereinat least one of the first pump input optical fiber and the second pumpinput optical fiber includes a fiber Bragg grating (FBG) configured tolock pump light received from the dual output laser diode to at leasttwo wavelengths.
 13. The dual fiber amplifier system of claim 12,wherein the at least two wavelengths are different from each other. 14.The dual fiber amplifier system of claim 11, wherein the active sectionis configured to generate pump light in response to injection of anelectrical drive signal into the active section, and wherein the pumplight is configured to propagate toward each of the first and second endfacets.
 15. The dual fiber amplifier system of claim 11, wherein one of:a reflectivity of the first end facet is the same as a reflectivity ofthe second end facet, and a reflectivity of the first end facet isdifferent than a reflectivity of the second end facet.
 16. A method,comprising: injecting a first electrical drive signal into a firstactive section portion of a dual output laser diode, the first activesection portion positioned between a first end facet and a second endfacet of the dual output laser diode; injecting a second electricaldrive signal into a second active section portion of the dual outputlaser diode, the second active section portion positioned between thefirst end facet and the second end facet of the dual output laser diode;generating light in the first active section portion and the secondactive section portion of the dual output laser diode responsive to theinjection of the first electrical drive signal and the second electricaldrive signal; propagating the light toward each of the first end facetand the second end facet; and transmitting the light through the firstend facet and the second end facet.
 17. The method of claim 16, furthercomprising: coupling light transmitted through the first end facet intoa first pump input optical fiber of a first fiber amplifier; andcoupling light transmitted through the second end facet into a secondpump input optical fiber of a second fiber amplifier.
 18. The method ofclaim 16, wherein the transmitting the light through the first endfacets and the second end facet comprises transmitting at least 99% ofthe light that reaches the first end facet and the second end facet. 19.The method of claim 16, wherein the first active section portion and thesecond active section portion are optically isolated by a reflectivestructure.
 20. The method of claim 16, wherein the injecting a firstelectrical drive signal includes supplying the first electrical drivesignal across a first anode and a first cathode coupled to opposingsides of the first active section portion, and wherein the injecting asecond electrical drive signal includes supplying the second electricaldrive signal across a second anode and a second cathode coupled toopposing sides of the second active section portion.